Samuel Yates began, and this site continues, a database of the largest known primes. Primes in that database are assigned a proof-code to show who should be credited with the discovery as well as what programs and projects they used. (Discoverers have one prover-entry, but may have many proof-codes because they use a variety of programs...)
This page provides data on x21, one of those codes.
Code name (*): x21 (See the descriptive data below.) Persons (*): 2 (counting humans only) Projects (*): 0 (counting projects only) Display (HTML): Walker, Broadhurst Number of primes: total 3 Unverified Primes: 0 (prime table entries marked 'Composite','Untested', or 'InProcess') Score for Primes (*): total 31.5209
Below is additional information about this entry.
Display (text): Walker, Broadhurst Display (short): Walker & Broadhurst Database id: 345 (do not use this database id, it is subject to change) Proof program: unknown Entry last modified: 2020-06-04 22:20:14